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Patents - Ambiguity. AP&C Advanced Powders & Coatings Inc. v. Tekna Plasma Systems Inc.
In AP&C Advanced Powders & Coatings Inc. v. Tekna Plasma Systems Inc. (Fed CA, 2026) the Federal Court of Appeal dismissed a patent appeal, here concerning a decision "addressing allegations of infringement and invalidity of a pair of related patents".
Here the court addressed patent 'ambiguity':[3] The Federal Court was correct to observe at paragraph 325 of its reasons that the claims of a patent must define distinctly and in explicit terms the subject matter of the invention for which an exclusive privilege or property is claimed (subsection 27(4) of the Patent Act, R.S.C. 1985, c. P-4), and that failure to do so may render the patent invalid for ambiguity. The Federal Court was also correct to state at paragraph 328 of its reasons that the scope of a patent’s prohibition should be made clear so that members of the public may know where they can go with impunity, and that when the claims, read purposively in the context of the patent as a whole, and with a mind willing to understand, do not permit the skilled reader to understand what falls within the claim and what does not, the patent does not serve its notice function and becomes a "“patent of uncertain scope”" that is a "“public nuisance”" (Free World Trust v. Électro Santé Inc., 2000 SCC 66, [2000] 2 S.C.R. 1024 at paras. 41 and 42). The Federal Court was also fully aware of the general disinclination of the courts to find a patent claim invalid for ambiguity. The Federal Court did not misstate the law on ambiguity.
[4] After a thorough review of the patents in suit, the evidence, the applicable law and the parties’ submissions, the Federal Court concluded that the claims in issue were ambiguous because the skilled reader would not be able, as regards the 502 Patent, to distinguish between the depletion layer and the native oxide layer, and hence would not be able to determine whether the former was deeper and thicker than the latter, and as regards the 236 Patent, to determine the existence of a depletion layer or its parameters.
[5] In these conclusions, we see no error of law, no palpable and overriding error of fact, nor any error of mixed fact and law from which an error of law is extricable. The Federal Court explained its reasoning throughout and took proper account of the evidence before it. The Federal Court was entitled to reach the conclusions it did. The Federal Court also properly recognized the differences in the wording of the various claims of the patents in suit.
[6] We do not accept AP&C’s argument that the Federal Court could not properly conclude that the claims in issue were ambiguous because it was able to construe them. The Federal Court stated clearly that the claims in issue provided insufficient definition to understand their scope.
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